The present invention relates to a valve needle for an injection valve. German Published Unexamined Application No. DE-OS 40 08 675 describes a valve needle for an electromagnetically operable valve comprising an armature, a valve closing element and a sleeve-like connecting tube joining the armature to the valve closing element, which may be spherical, for example. The individual sections are individual parts manufactured separately and joined together by a joining method such as laser welding. The armature completely encompasses the connecting tube radially and at least partially axially, because the connecting tube is secured in a longitudinal through-bore in the armature. The connecting tube itself also has a longitudinal inside through-hole in which fuel can flow in the direction of the valve closing element and then come out close to the valve closing element through radial cross-holes provided in the wall of the connecting tube. Fuel thus flows first inside the valve needle, leaving the valve needle positioned only toward the valve seat.
In addition, U.S. Pat. No. 4,610,080 describes a valve needle in a fuel injection valve which is designed in two parts. A pot-shaped armature is fixedly connected to an elongated metal rod-shaped connecting part on whose downstream end is shaped directly a valve closing body in the form of a spherical section. A connecting sleeve having an internal opening extends out of the bottom part of the pot-shaped armature. The inside opening is provided with several grooves following one another at a distance axially, resulting in successive areas of larger and smaller diameters in the opening. The connecting part projects with its end opposite the valve closing body, which is also grooved and is opposite the valve closing section, into the opening in the connecting sleeve, so the two metal parts are joined together in a form-fitting manner.
German Published Unexamined Application No. DE-OS 195 03 224 describes a three-part valve needle for electromagnetically operable injection valves formed by a tubular armature, a sleeve connector part and a spherical valve closing body. The connecting part made of plastic engages with catch elements on the outer periphery of the armature to provide a secure connection of the armature and the connecting part. The downstream end of the connecting part has a cup-shaped recess in which the spherical valve closing body is snapped or clipped. The bottom part of the recess is so elastic that it widens when the valve closing body is pressed into it, then encircles the valve closing body tightly.
The valve needle according to the present invention can be manufactured especially easily and inexpensively. Each individual part of the valve needle, namely an armature, a valve closing element and a connecting part that connects the armature to the valve closing element, can be manufactured and machined especially inexpensively because of their very simple contours. The connecting part made of a plastic ensures a lower weight of the valve needle in comparison with metal valve needles. Especially with injection valves having a delivery point that is shifted especially far forward, where relatively elongated valve needles are used, very good dynamic valve properties can be achieved through such a design of the connecting part. The damping properties of the plastic also ensure reduced noise generation. In an advantageous manner, the valve closing element and the connecting part designed according to the present invention have a small outside diameter, so that an injection valve with such a valve needle can be designed to be very slender. The form-fitting connection of the valve closing element and the connecting part designed according to the present invention can be achieved in an especially simple manner and is nevertheless very secure. The possibility of detachment during the axial movement of the valve needle inside the injection valve is completely ruled out with this connection method.
It is especially advantageous that inexpensive bar stock is used for the connecting part, which can be adjusted very easily to an exact length for use on the valve needle in accordance with a desired valve length. In this way, valve needles for injection valves having a delivery point shifted far forward can be designed very easily. The connecting part, which is made of solid plastic, has the advantages of a small outside diameter because no internal flow orifices are provided, and therefore it also has a low mass. The valve needle, which is designed to be very slender, permits an especially narrow design of the injection valve, in particular a reduction in the size of the valve seat body in comparison with known injection valves.